Taking HIV treatment and having an undetectable viral load associated with unprotected sex in Switzerland

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The 'Swiss Statement' about the impact of antiretroviral treatment on infectiousness appears to have had an impact on the sexual behaviour of HIV-positive individuals in that country.

In the December 1st edition of Clinical Infectious Diseases investigators report an association between taking HIV treatment that is reducing viral load to undetectable levels and unprotected sex. The proportion of individuals reporting sex without a condom with their main partner increased after January 2008 when senior Swiss doctors published their statement about the impact of effective HIV treatment on infectiousness.

“In contrast to earlier results from our cohort, which did not find an association between viral load and sexual behaviour, we now observed an association of a suppressive ART [antiretroviral therapy] and unprotected sexual contacts in MSM [men who have sex with men] and heterosexual women with stable partners, indicating that some groups with HIV infection have adopted the belief that treatment of HIV infection is a sufficient HIV-prevention measure,” write the investigators.


Swiss statement

A 2008 article by a group of Swiss doctors which asserted that people living with HIV who are taking antiretroviral therapy and have an undetectable viral load, with no sexually transmitted infections, do not pass on HIV to their sex partners. Since then, major scientific studies have proven that the statement was correct.


The fluid portion of the blood.


A serodifferent couple is one in which one partner has HIV and the other has not. 

mother-to-child transmission (MTCT)

Transmission of HIV from a mother to her unborn child in the womb or during birth, or to infants via breast milk. Also known as vertical transmission.


Choosing sexual partners of the same HIV status, or restricting condomless sex to partners of the same HIV status. As a risk reduction strategy, the drawback for HIV-negative people is that they can only be certain of their HIV status when they last took a test, whereas HIV-positive people can be confident they know their status

An editorial that accompanies expresses some alarm about individuals making decisions about the use of condoms on the basis of their viral load. The author notes that infections have been attributed to patients taking HIV therapy who have an undetectable viral load, and that the understanding of the impact of HIV treatment on infectiousness is still incomplete.

In January 2008 a group of senior HIV doctors in Switzerland published what has become known as the Swiss Statement.

This said that HIV-positive heterosexuals could discontinue condom use with their regular HIV-negative partner if:

  • Their partner agreed.
  • They were taking HIV treatment.
  • Their blood viral load had been undetectable for at least six months.
  • They did not have any other sexually transmitted infections.

Considerable controversy has surrounded the statement. There is a general consensus that taking HIV treatment substantially reduces the risk of sexual transmission of the virus. Nevertheless, many researchers believe that a low risk of transmission persists.

Swiss investigators wanted to see if factors such as taking HIV treatment, viral load, and drug and alcohol use were associated with unprotected sex in their cohort of patients.

They therefore analysed self-reported condom use for 7309 patients between 2007 and 2009. The patients were divided according to their HIV risk group: gay and other men who have sex with men; heterosexual men and women; and injecting drug users.

Information was obtained on condom use with regular and casual partners.

Investigators were also eager to see if the issuing of the Swiss statement had lead to changes in reported condom use. Other Swiss research has shown that about a quarter of gay men are using unreliable HIV risk reduction strategies such as serosorting or strategic positioning. The authors of this study noted that these risk-reduction methods have never been promoted in Switzerland.

A total of 80% of patients were taking HIV treatment, and 82% of these individuals had an undetectable viral load.

Overall, sex with only one stable partner was reported by 46% of gay men, 80% of heterosexual men, 91% of heterosexual women, and 75% of injecting drug users.

Having both a regular and casual partners was reported by 18% of gay men, 4% of heterosexual men, 1% of heterosexual women and 3% of injecting drug users. In total, 37% of gay men said they only had casual partners, as did 17% of heterosexual men, 8% of heterosexual women and 22% of injecting drug users.

Regular condom use was reported by 89% of individuals with a regular HIV-negative partner and by 48% of those whose partner was also HIV-positive. In all four HIV risk groups, rates of consistent condom use were lower with regular partners than casual partners (88 vs 92%, p < 0.001).

Factors associated with unprotected sex were:

  • For all groups, time period after the release of the Swiss Statement.
  • An undetectable viral load for gay men (OR, 2.41; 95% CI, 1.35 to 4.30) and heterosexual women (OR, 2.73; 95% CI, 1.87 to 3.99) with a stable partner.
  • Younger age.
  • Moderate to severe alcohol use for heterosexual women and injecting drug users with stable partners and heterosexual men with casual partners.
  • Any illicit drug use for gay men and heterosexual women with stable partners, and gay men, and heterosexual men and women with casual partners.

The investigators focused on the impact of the Swiss Statement on reported condom use with regular partners.

They found that even before the issuing of the statement, there was already a progressive increase in the proportion of gay men and heterosexual women reporting unprotected sex with their stable partner.

However, the release of the statement was followed by a decline in reported condom use by individuals with an undetectable viral load.

Gay men (OR, 2.81; 95% CI, 1.37 to 5.80), heterosexual men (OR, 1.58; 95% CI, 1.00 to 2.48) and heterosexual women (OR, 2.14; 95% CI, 1.43 to 3.22) whose viral load was undetectable were all significantly more likely to say that they had had unprotected sex with their main partner after the issuing of the statement.

“The effect of the ‘Swiss Statement’ was most pronounced in groups with stable partners who had an undetectable viral load,” comment the investigators. They believe that their patients were able to accept the “complex recommendations” of the statement.

The investigators also note that the release of the statement and the subsequent change in sexual behaviour by their patients  did not lead to an increase in observed new HIV infections in Switzerland.

They conclude that “because ART influences sexual behavior in HIV serodifferent partners, adherence to treatment and plasma viral load should be regularly monitored in the HIV-positive partner, and counselling of couples should be advocated".

Such counselling should be individualised, and account should be taken of drug and alcohol use.

Dr Myron Cohen, author of the editorial that accompanied the study, said that there is “every reason to pause and reflect” about the actual impact of HIV treatment on infectiousness. “The protection provided from ART is not absolute and is not absolutely predictable,” he writes.

Cohen also notes that there are many unanswered questions about the infectiousness of people taking suppressive HIV treatment. These include the risk of transmission over time; the impact of different HIV treatment combinations on infectiousness; and the risks involved with anal and vaginal sex.

The author also notes that investigators “painstakingly” defined their recommendations about the impact of HIV therapy and viral load on the risk of mother-to-child transmission. He hopes that similar data will direct the use of HIV treatment as prevention.


Hasse B et al. Frequency and determinants of unprotected sex among HIV-infected persons: the Swiss HIV Cohort Study. Clin Infect Dis, 51: 1314-1322, 2010 (click here for access to free abstract).

Cohen MS HIV treatment as prevention and the “Swiss Statement”: on for a dime, in for a dollar? Clin Infect Dis 51: 1323-24, 2010 (click here for access to the for-free text).